The present invention relates to a geological probing device comprising a hollow probing rod to be extended into the geological matter to be probed, and a measuring probe fitted to the probing rod, the measuring probe comprising at least one sensor for obtaining information (e.g. physical and chemical characteristics) about the matter (e.g. soil or rock).
Such probing devices can be implemented in Cone Penetration Test (CPT) equipment, and are primarily used in geotechnical investigations, but can also be used in geological investigations in general, on and off shore.
A probing device of this kind is shown in U.S. Pat. No. 5,902,939. A drive mechanism is provided to push the probing rod into the soil, for example using hydraulic force. During operation, the probing rod is extended one section at a time, whereby each new section is linked to the sections of the probing rod already pushed down, for example by means of screw threads in the ends of each section. Preferably, the process of linking sections together can be performed without interrupting operation of the drive mechanism.
A measuring probe is fitted to the probing rod, preferably close to the tip of the rod, and can be adapted to measure friction, probe inclination, water pressure, etc, using one or several sensors. At the surface, processing and recording equipment is arranged to receive data from the probe.
When using probing devices of this kind, the data from the probe can be transmitted to the equipment at the surface using different techniques.
In the probing device mentioned above, the data is transmitted by means of a electrical or optical cable, running through the hollow probing rod. Such a cable complicates the process of linking rod sections during operation.
According to another known technique, the data is transmitted using acoustic signals, propagating through the material of the probing rod. A drawback with this solution is the transmitted signal""s sensitivity to noise in the ground, caused by e.g. heavy equipment on the surface and the friction against the probing device itself. Also, the qualities of the soil has an important impact on the transmitted signal. Too much noise makes it difficult to process and analyze the acquired data.
A third solution is presented in EP 1065530, describing optical transmission of data. In this case, each section of the probing rod is provided with one or several optical guides located inside the hollow probing rod section. The optical guide section is in the form of a glass or plastic rod, or one or several optical fibers. When the rod sections are linked together, a continuous optical guide is formed, allowing transmission of optical signals from the probe to a receiver located at end of the probing rod, normally above the surface.
Although this solution eliminates the need for providing a cable into the rod, it complicates the linking of rod sections, as care has to be taken not to disrupt the optical guide. Also, the probing rod sections become more expensive, and also more sensitive to environment and treatment. Additionally, the process of receiving the optical signals is very delicate, and can easily be interrupted. Notably, the optical link will be interrupted each time a new rod section is linked to the probing rod. EP 1065530 attempts to solve such problems, including memory units, optical mirrors, camera based sensors, etc, resulting in a complex and costly probing device. It is considered that such an optical system is badly suited for the conditions present during soil probing.
Therefore, it is an object of the present invention to provide an improved geological probing device, alleviating the above mentioned problems.
More specifically, it is an object of the invention to provide an improved data transmission in a geological probing device.
These and other objects are accomplished by a geological probing device of the kind mentioned by way of introduction, wherein the measuring probe further comprises a microwave transmitter, arranged to transmit microwaves carrying data from said sensor, and wherein the hollow probing rod is adapted to act as a waveguide, guiding the microwaves to an upper orifice of said hollow probing rod.
According to the invention, the interior of the probing rod is thus employed as a waveguide, through which the microwaves can propagate from the probe to the upper orifice, located above or close to the surface. Conventional probing rods, typically made of steel, offer satisfactory wave guiding characteristics in the micro frequency range, and no particular preparation of the probing rod therefore needs to be performed.
It should be noted that the term xe2x80x9chollowxe2x80x9d refers to the rod itself. In other words, the hollow space may well be filed with some material other than air, such as a suitable dielectric material, e.g. Teflon.
Compared to previously known techniques, the device according to the invention offers a reliable transmission of data under normal working conditions, and without substantial modifications of the probing rod. In fact, a conventional probing device can be adapted to the invention, by being provided with a microwave transmitter and a suitable interface(s).
Compared to acoustic transmission, the inventive device is less vulnerable to unpredictable sources of disturbance, such as characteristics of the geological matter and surroundings. Instead, the transmission of microwaves depends on factors inherently present in the device itself, such as the inner surface of the probing rod.
Compared to optical transmission, a micro wave based system is more robust, and signals will not be interrupted as easily. Although microwaves, like optical waves, cannot penetrate objects in their path, they are more easily reflected in e.g. the frame of a penetrometer, and can therefore often reach a receiver despite objects being placed in between.
The probing rod can be formed by a plurality of rod sections, arranged to be linked together one by one during extension thereof into the geological matter. This offers flexibility when extending the probing rod deep into the ground or sea bed. As mentioned, the microwaves will be spread and reflected when they leave the upper orifice of the rod, and a linking of an additional rod section will therefore only cause a minor disruption in signal reception.
Preferably, the device comprises a receiver at a location outside said upper orifice, adapted to receive the microwaves propagated through the probing rod. The receiver can comprise several receiving units, with different polarization, in order to further minimize disruptions of the signal caused e.g. when linking a new rod section, and to improve reception in general. The microwaves can have a frequency in the range 2-300 GHz, and preferably in the range 5-30 GHz. The most suitable frequency primarily depends on the characteristics of the probing rod (section shape, diameter) acting as a waveguide. In principle, a lower frequency wave requires a larger diameter waveguide. Further, some frequencies (e.g. the 5.6 GHz-band, the 24 GHz-band) are more convenient, as they do not require the end user to have permission from the national telecommunication authority, as long as the equipment is certified.
The geological matter can be soil, such as sand, clay, silt, and the probing rod can then be pushed into the soil using e.g. a hydraulic drive mechanism.
Alternatively, the geological matter can be rock, in which case the probing rod can be equipped with a suitable drilling point and be drilled into the rock.
The probing device can be used in all types of geological investigation, including geotechnical investigations on land, and off-shore investigations.